Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Volts Set meter to measure AC Volts
Draw back rubber shroud covering the flame sense electrode and lead
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Press Reset to cancel purge cycle countdown.
Ensure there is no demand.
Measure the voltage between the flame sense electrode and a suitable Earth.
Expected voltage approximately 91 VAC.